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From Chuck Murcko <ch...@topsail.org>
Subject Re: [PATCH] buff.c bug fix
Date Sat, 25 Jan 1997 12:51:07 GMT
Dean Gaudet wrote:
> 
> On Fri, 24 Jan 1997, Roy T. Fielding wrote:
> 
> >   * report from some folks at w3c.org about pipelined requests
> >        Info: http://www.w3.org/pub/WWW/Protocols/HTTP/Performance/Apache.html
> >        Status: deferred til after 1.2b5, maybe beyond 1.2
> 
> I've been looking into this one.
> 
> So far I can see a definite bug in bcwrite().  It's probably due to
> the assumption that if r=write(f,b,n) then r is one of -1, or n unless
> f is non-blocking.  That isn't the case, all values -1 <= r <= n are
> possible for any f.  I notice later on in bwrite() that it also indicates
> that assumption... but the bwrite() code looks ok on my first reading.
> 
> In particular, looking through the linux kernel code (the w3 report used
> linux 2.0.18 for the server) I notice that it's possible if the tcp stack
> can't get memory during a write() and has to block to do it but received
> an unblocked signal then it returns a partial write().  There are also
> other cases that will return partial write()s.
> 
> Included is a patch that fixes bcwrite().  (A better performance patch
> would use writev() to write the three pieces.)  I've lightly tested it...
> although I'm not really sure how to test chunked encoding.
> 
> Also included in this patch is a performance fix for a case where bwrite()
> would return while having a full buffer.
> 
> Plus a fix to remove an unused variable in bflush().
> 
Very nice. +1 if this passes Henrik's muster.

I don't think this is the cause of all the slowness of 1.2 relative to
1.1, though. I suspect it's time to think about a hashed child status
list. I think we'll find most of the slowness there. Randy, did you ever
try profiling without mod_status in the mix?
-- 
chuck
Chuck Murcko
The Topsail Group, West Chester PA USA
chuck@topsail.org

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